[scraperhelper] Allow scraper controller to be configured to run scrapers in parallel

[dehaansa]

Description

When investigating an issue in contrib, it was discovered that the scraperhelper did not have a way to run scrapers in parallel and take advantage of the connection pool in the sqlqueryreceiver. This PR adds the ability to configure the scrapercontroller to run either unbounded goroutines to scrape in parallel or a configurable size worker pool for running scrapers in parallel.

Link to tracking issue

Fixes #13113

Testing

Unit tests updated, but otherwise untested, posting here for initial review while I evaluate in context in contrib.

Documentation

No docs updated, as there's no existing docs for the package.

[codecov]

Codecov Report

Attention: Patch coverage is 92.74194% with 9 lines in your changes missing coverage. Please review.

Project coverage is 91.27%. Comparing base (e1a9093) to head (c06c27c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
scraper/scraperhelper/controller.go	92.74%	8 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (92.74%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13167      +/-   ##
==========================================
- Coverage   91.27%   91.27%   -0.01%     
==========================================
  Files         510      510              
  Lines       28758    28858     +100     
==========================================
+ Hits        26250    26341      +91     
- Misses       1993     2001       +8     
- Partials      515      516       +1     

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[josepcorrea]

Hi! I'm currently working with the sqlqueryreceiver and very interested in testing this new parallel scraping feature — especially the worker pool mode. I can validate behavior and performance improvements when multiple queries are involved and connection pooling is in place.

Let me know if there’s anything specific I should focus on during testing, or if you'd prefer feedback via issue or PR comments. Thanks for the great work!